1. Field of the Invention
The present invention relates to a method of coring a crustal core sample, which is useful for, for example, researches on intracrustal microorganisms in the crustal core, and antimicrobial polymeric gel and a gel material used in this method.
2. Description of the Background Art
In recent years, researches on crustal interiors have been progressed, and a presence of subterranean microorganisms under a deep, high-temperature and high-pressure environments in the crustal interior has been reported. According to researches on intra-crustal microorganisms in a subterranean microbial sphere composed of these subterranean microorganisms, there are important hidden possibilities such as elucidation of influences of material conversion and mass transfer in a deep geological environment for example, and further, elucidation of origin of life on the primitive earth and evolution thereof, or development of drugs and novel materials.
A crustal core sample can be taken with comparative ease from the crust at the depth closer to mantle by drilling crust of sea bed by means of, for example, a drill ship. As an example of a method for conducting the drilling using the drill ship, for example, a riser drilling method has been known. In this method, a drill pipe extending from the drill ship to the sea bed is rotated to drill the crust by means of a drill bit provided on the tip thereof and at the same time, to feed circulating fluid such as drilling mud or sea water, in which the specific gravity, viscosity, chemical composition, etc. have been adjusted according to the condition of the crust drilled, to the drill bit.
A crustal core sample obtained by such a method has a great possibility that the state of the sample present in the crust as it is may be lost by an influence exerted from the outside during the coring operation, for example, by causes such as its contact with the circulating fluid. In such a case, there is a possibility that the crustal core sample obtained may become useless for various research objects.
In order to deal with such a problem, a method in which when a crustal core sample is cored, the surface thereof is coated with non-invasive gel, thereby obtaining the crustal core sample in a state that its physical structure has been protected from the external factor is disclosed in U.S. Pat. No. 5,482,123.
In this method, however, there is a possibility that adventitious heterogeneous microorganisms may permeate the gel coat on the surface of the core sample to enter the interior of the gel coat, thereby adhering to the crustal core sample. The microorganisms adhered, then may possibly grow on the surface or in the interior of the crustal core sample.
In the handling of the gel forming the surface coat, it is extremely difficult to prevent the gel from being contaminated with the microorganisms because the microorganisms unavoidably adhere to the gel itself.
The crustal core sample contaminated with the adventitious heterogeneous microorganisms by the above-described cause or any other cause becomes unsuitable for use in researches on intracrustal microorganisms.
As described above, according to the conventional method for coring a crustal core sample, measures against the microbial contamination by mixing of the adventitious heterogeneous microorganisms or growth thereof are insufficient. Therefore, the crustal core sample taken by such a method involves a problem that the sample is not fully suitable for use in researches on intracrustal microorganisms.